To make the dark chocolate layer, place the dark chocolate, miniature marshmallows, milk, and salt into the top of a double boiler over medium heat. Stir until chocolate melts and mixture is smooth. Remove from the heat, and stir in the vanilla. Allow to cool, stirring occasionally.
Beat the heavy cream in a bowl until soft peaks form. Fold the whipped cream into the dark chocolate mixture until evenly blended. Spoon the mixture into the prepared graham cracker crust. Spread 1/2 chocolate whipped topping over the dark chocolate layer. Refrigerate at least 30 minutes.
Meanwhile, make the milk chocolate layer by placing the milk chocolate, miniature marshmallows, milk, and salt into the top of a double boiler over medium heat. Stir until chocolate melts, and mixture is smooth. Remove from the heat, and stir in the vanilla. Allow to cool, stirring occasionally.
Beat the remaining 1/2 cup heavy cream in a bowl until soft peaks form. Fold the whipped cream into the milk chocolate mixture until evenly blended. Pour the mixture over chocolate topping layer. Spread the remaining chocolate whipped topping over the milk chocolate layer. Spoon the whipped topping over the chocolate topping. If desired, garnish with miniature chocolate chips.
